A type of base station called a femto (Femto) base station is known. One example of a femto base station forms a femtocell that has a coverage area radius (several meters to several tens of meters) smaller than that of a macrocell (1 kilometer to several kilometers in radius). A femto base station is used in blind areas (e.g., areas above and below ground) and confined areas (e.g., households, offices, or facilities) for providing users with services.
With usage of a femto base station, radio waves can cover difficult-to-cover areas, such as areas inside a building. Although each area is small, if many base stations are installed and the number of mobile terminals per cell is decreased, connectability increases, which enforces the backbone for supporting service providing.
Japanese Laid-open Patent Publication No. 2007-274208 discloses a power-saving base station. Japanese Laid-open Patent Publication No. 2007-274208 describes a base station that calculates the number of mobile terminals that are currently in a position to make communications with the base station by comparing the identification number of any mobile terminal that has been detected by a sensor with a list of the identification numbers of mobile terminals able to make communications with the base station and shifts to a power saving mode in accordance with the number of the mobile terminals.
Japanese Laid-open Patent Publication No. 2002-158609 discloses a base station that reduces the power consumption by shifting to a power saving mode during a time zone when the line utilization rate decreases and then intermittently transmitting broadcast information, etc. Japanese Laid-open Patent Publication No. 7-336768 discloses a radio communication device in which, if the access frequency of a mobile terminal that is in the service area decreases, a first base station stops and a second base station increases both its output power and receiver sensitivity, thereby making communications with a mobile terminal in the radio area of the first station.
However, according to the above power-consumption reducing technologies, when a mobile terminal makes no communications with a base station but the mobile terminal is present in the femtocell that is formed by the base station, there is a possibility that the base station cannot shift to the power saving mode. This leads to a problem in that, even if the above power-consumption reducing technologies are used in a femto base station, there is a possibility that the power consumption of the femto base station is not decreased to its lowest. The problem related to the power consumption arises with not only femto base stations but also other base stations (macrocell base station).